Process for burning powdered fuel.



H. LLDOHERTY.

PROQESS FOR BURNING POWDERED FUEL. APPLICATION FILED 050.31, 1909..

1,145,356. Pat ente d July 6, 1915.

Hgnruv L. Duherty, Svwwtoz HENRY I. D OHERTY, OF NEW YO'R'K, N. Y.

PROCESS FOR BURNING POWDERED FUEL.

Specification of Letters Patent.

Patented July 6, 1915.

Application filed December 31, 1909. Serial No. 535,844.

ments in Processes for Burning Powdered Fuel, of which the following is a specification.

This invention relates to a burning powdered fuel. 0

The objects of my invention are, firstly, the obviating of the danger of explosion in the fuel feed-pipe conveying the powdered fuel to the furnace, and secondly the regu lation of the combustion so that the temperature produced may be controlled to any desired extent, thereby permitting the use of powdered fuel for low temperature operations and avoiding the burning out of furnaces, which latter is a common result of the ordinary methods of firing with powdered fuel.

My invention, briefly stated, consists in process for the substitution of inert or non-oxidizing gases-such as flue gas -for air, as the vehicle in which the powdered fuel is carried into the furnace, the said flue gas being supplied under pressure and the mixture of flue gas and powdered fuel discharged into the combustion chamber through an appropriate inductor passage, whereby the air necessary for the combustion of the fuel is drawn into the inductor so that the combustion. gases are substantially free from significantly reactive amounts of uncombined oxygen' The volume of the flue gas used as the fuel-conveying medium is varied according to the temperature desired in the furnace-or, rather, according to the flame temperature desired. The presence of the flue gas in the flame acts in two ways. In the first place, it retards the velocity of re action by lowering the partial pressure of the oxygen in the initial combustible mixture, and by its mechanical eifect in dilut= ing the oxygen so that an appreciable time is required before the carbon particles come into reactive proximity with suflicient oxygen molecules for their combustion, and in the second place it adds to the combustion mixture a large volume of inert gas whose temperature must be raised by the heat of the reaction as well as that of the normal combustion gases. The first effect causes the combustion to take place w1th a comparatively slowburning dilated flame while the second-effect causes a diminution in the normal flame temperature commensurate with the volume of flue gas relative to the air. The precise volume of flue gas used to carry the powdered fuel per pound of the latter will vary according to the temperature desired in the furnace, the nature.

and quality of the fuel, etc., aswell as the quality of the flue gas itself,i. e..according to the proportion of CO in the latter.

In the usual method of burning powdered fuel it is necessary to usea very large excess of air in order that the flame. temperature shall not be sufficiently high to cause fluxing of the furnace walls. This practice produces a flue gas which may contain by volume as much as,14:% of free oxygen.

Such a gas is not suited for use in my process. I find that by my method of conduct ing the combustion I am enabled to secure a practically complete combustion with a very small excess of air. With proper regulation and provisionagainst leakage of air into the furnace'I find that the volume of' flue gas per pound of carbon mayadvantageously be between 60 and 200 cu. ft. (normal). The former givinga'high flame temperature, while with the latter quantity the flame temperature is reduced to about that given by a poorproducer gas.

In the accompanying diagrammatic drawings I have shown a form of apparatus iciapable of applying my process to boiler rlng.

Figure 1 shows an arrangement whereby the powdered fuel andflue gas are mixed, while Fig. 2 shows the method of introducing the fuel-current into the furnace of a boiler. Fi 3 is a part elevation of the front of a single boiler showing the burners, and position of the fuel conduits.

1 indicates a blower whose suction pipe, 2, isconnected to some source of flue, or other non-oxidizing gases-in the present case, the main flue of the boiler plant.

3 is the discharge pipe of the blower which is'connected to a nozzle-shaped fuel I 105 the b ower serves to regulate the volume of flue gas discharged by blower 1. The powdered fuel is fed into 7 by conveyor 6, and is taken Into suspension by the current of flue gas passing through d. The fuel laden current of flue gas thence passes through the conduit 9, and is distributed to the furnaces. p r V The proportion of flue gas to fuel whlch I use depends upon the nature of the operation which I WlSh to carry out; or, 1n other words, upon the flame temperature which I wish to produce. For boiler'firing, it isonly necessary to use sufiicient flue gas to bring the flame temperature down to about 2700" flue gas to fuel is necessary.

' ,of flue gas, as it is manifest that this may be varied to suit the conditions it is desired to obtain, I may say, that for ordinary furnace operations, I use from 60 to 200 cu. ft. of flue gas'per lb. of powdered fuel, the minor proportion being used for'hlgh temperatures and the major for low flame temperatures.

The fuel laden current of flue gas passes through the main conduit, 9, to the connections. 10, 10'', 10", etc, of the boiler furnaces. In the form of burner figured, 11 is the burner tube, proper, which is com- I posed, preferably, of some hi hly refractory material such as fire-clay. he fuel-laden current of flue gas is discharged throughthe nozzle, 12, the volume of the fuel current being regulated by the valve 13. Air for combustion is admitted through damper 14;, whichmay be of any suitable ty c.

From the arrangement 0 apparatus shown, it is obvious that the current of flue gas laden with powdered fuel will discharge intothe combustion chamber as a truncated .conical body surrounded with an envelop of air, which latter is drawn in through the damper 14: and the annular passage of burner 11 surrounding the nozzle 12. The initial combustion therefore takes place over the conical surface of v the flue gas body-the fuelladen. flue gas and air gradually mixing as the two currents flow through the combustion chamber, the initial conical annulus of flame gradually changing into a diffused ame with the increase in the distance from he point of introduction. By this method ofintrod'ucing the powdered fuel separate messes 'fiom the air, the former is only exposed to oxidizing conditions gradually, although the temperature of-the combustion chamber into which it is introduced is far above its ignition temperature. There is'thus exerted a retarding eflect upon the combustion in addition to that exerted by the presence of the flue gas, and it is possible to prolong the flame to a greater extent, with a given proportion of flue gas, than would be otherwise possible. 4

Suitable settling chambers (not shown) should be provided either in the flue connections of the individual boilers or at the base of the stack. Suitable cleaning doors should also be provided to give access to the bottom of the furnace chambers and to the flue gas conduits. The flue gas connection from the blower should be made to the flue gas conduits after the settling chambers.

Having described my invention, what I claim is: v

1. The method of burning powdered fuel which comprises sus' ending said powdered fuel in an accelerate bustion gases, said draft current containing a less proportion of free oxygen than that required to form. a combustible mixture with said powdered fuel, and discharging the fuel-laden draft current into a combustion chamber in such manner as to induct air into said chamber as a conical annulus surrounding said fuel-laden draft current the volume of induced-air required for .the combustion of the fuel carried by the said draft current, whereby the said fuel-laden draft current is caused to mix gradually with said air to produce a prolonged combustion.

2. The method of burning powdered fuel which comprises, suspending the said powdered fuel in a draft current of combustion gases substantially free from a significant excess of uncombined oxygen, introducing the said fuel-laden draft current into a combustion space maintained at an igniting temperature, introducing into said. combustion space as a separate draft current suflicient air to burn said powdered fuel, the air current'being introduced as an annular gaseous body enveloping said fuel-laden draft cur-' rent, whereby a slow combustion of said draft current of compowdered fuel is caused with the production of a prolonged flame.

Signed at New York city-in the county of New York and State of New York this 30th day-of December A. D. 1909.

HENRY LDOHERTY. Witnesses:

W. J. QUENTIN, Time. I. CARTER. 

